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ABSTRACT: Practical Applications of the Ground-roll Inversion
Estimation of the near-surface shear-wave velocity structures is very important for different petroleum as well as non-petroleum purposes. Shear-wave velocities can be derived using the ground-roll inversion method. We have used the Multichannel Analysis of Surface Waves (MASW) method to estimate those velocities. This method is based on the frequency-dependent properties of the ground-roll. Once the high-resolution shear-wave velocity structure is estimated then it can be applied for various practical purposes. In this paper, some of those applications (density prediction; and statics estimation) have been presented. A proper knowledge of two important rock properties - seismic velocity and bulk density can be very helpful in estimating the reflection coefficients and hence generating synthetic seismograms. If density information is unavailable then it can be predicted by using Gardner’s relation. We used a modified Gardner’s relation to predict bulk densities from shear-wave velocities estimated from noninvasive ground-roll inversion method. Different types of seismic data sets have been used- i) Modeling data (numerical and physical modeling);and ii) Field data: Red Lodge, Montana, and the Meteor Crater, Arizona. Predicted densities are consistent with known values with maximum error of 0.5 gm/cc. We find exponential values for the modified Gardner’s relation formula varying from 0.21 to 0.234 while the suggested value is 0.22. The prediction of bulk densities for varied materials maintains a confidence level of above 90 %. Another important application of the ground-roll inversion is the calculation of the simple shear-wave statics which can be used during the multicomponent seismic analysis. For highly complex, unconsolidated, low-velocity near-surface of the Meteor Crater site, the simple shear-wave statics are calculated which vary between 40 to 70 ms for a 45 m deep model.